Fast Charge Separation at Semiconductor Sensitizer–Molecular Relay Interface Leads to Significantly Enhanced Solar Cell Performance

We report on an effective strategy to improve the efficiency and stability of liquid junction semiconductor-sensitized solar cells employing cobalt bipyridyl complex-based electrolyte. With CdS-sensitized TiO2 as a model system, we demonstrate that grafting the surface of CdS with small relay molecule, 4′-(bis(4-(hexyloxy)phenyl)amino)biphenyl-4-carboxylic acid (PAPC), drastically improves the cell performance and leads to an unprecedented power conversion efficiency. Transient absorption measurement indicates the photogenerated holes in CdS could be instantaneously intercepted by the grafted PAPC molecules, which greatly facilitates the charge separation and thus stabilizes CdS. We believe such a concept could be applied to other semiconductor sensitizers, especially for those with superior light absorption, such as CdSe, CdTe, etc.